Nitro steel was introduced in 1898 for the No. 3 and Pigeon and later the No. 4 and No. 5, and was certainly a high quality steel of the day; similar (if not the same) to Parker Titanic offered for Grades 3 - 6 from 1897 until the introduction of Acme steel for Grades 4 - 6 around 1910.
I have not composition tested a chunk of Nitro steel, but a summary of vintage barrel steel strength and composition is here
If someone has a junker Nitro steel barrel I would very much like to tensile and composition test a segment.